1. Field of the Invention
Aspects of the present invention relate to a thin film transistor, a method of fabricating the same, and an organic light emitting diode (OLED) display device including the thin film transistor. More particularly, aspects of the present invention relate to a thin film transistor in which a first insulating layer is formed with a predetermined thickness on a gate electrode, followed by ion doping. In this way, an offset region may be formed aligned with the gate electrode without a need for an additional spacer, and the thickness of the first insulating layer can be varied to facilitate adjustment of the width of the offset region. Additional aspects of the present invention include a method of fabricating the thin film transistor, as well as an OLED display device using the same.
2. Description of the Related Art
In general, polysilicon layers are widely used as semiconductor layers of thin film transistors because of the layers' high field effect mobility and applicability to high-speed operating circuits and CMOS circuits. A thin film transistor using a polysilicon layer may generally be used as an active element of an active matrix liquid crystal display (AMLCD), and a switching element and a driving element of an organic light emitting diode (OLED).
In a thin film transistor using such a polysilicon layer, ion doping may be performed on predetermined regions of the polysilicon layer to form source/drain regions. Here, strong electric fields may be formed at interfaces between channel regions on which ion doping is not performed and drain regions on which ion doping is performed to generate leakage currents or hot carriers, and the generated currents may move towards the channel, causing performance characteristics of a device to degrade.
In order to overcome such drawbacks, a method of forming a low-concentration doping region or an offset region between the channel region and the source/drain regions has been proposed. A conventional method of forming an offset region may include forming a spacer on a lateral surface of a gate electrode and then ion doping on the structure. The spacer may be created by forming an insulating layer on the gate electrode and patterning the resulting structure or by performing anodic oxidation. However, in order to form the spacer using these methods, an additional mask and a photo process for patterning may be required or the manufacturing processes may be more complex because of the anodic oxidation process.